Gerotor devices operate with a pressure differential between an input port and an output port. A gerotor motor uses this pressure differential to turn a shaft. Because of this pressure differential, a pressure imbalance may occur within the gerotor device. For example, in a gerotor motor having rotor valving, high pressure fluid passing through the rotor forces the rotor away from valving plates, which are adjacent to a forward face of the rotor. This separation reduces the efficiency of the gerotor motor and also increases wear on the rear face of the rotor, which is opposite to the forward face.
U.S. Pat. No. 4,717,320 describes a gerotor motor that overcomes the problems associated with the aforementioned pressure imbalance. A balancing plate structure that biases the rotor back against the valving plates is described. The balancing plate structure includes an annular cavity that is pressurized with hydraulic fluid to bias a balancing plate, which moves the rotor towards the valving plates. When only one relief hole is provided, as described in U.S. Pat. No. 4,717,320, pressure can remain in the annular cavity when the rotor stops and the relief hole is not aligned with a relief groove formed in the rotor. This results in the balancing plate pressing against the rotor in an axial direction. If this pressure is not released, then the balancing plate operates like a brake and impedes rotational and orbital movement of the rotor. When the motor is restarted, the pressure in the fluid pockets defined by the rotor must overcome this “braking” force before the rotor can begin its rotational and orbital movement.